0DTE — same-day-expiration options on the S&P 500 — went from a niche product in 2020 to over 45% of total SPX option volume by 2026. That structural shift quietly rewrote how intraday volatility behaves. If you trade SPX, SPY, or ES futures, you're trading inside the gamma surface that 0DTE creates whether you realize it or not.
The mechanical setup
A 0DTE option dies at end of day. Its gamma — the second derivative of price with respect to spot — is enormous near the strike and collapses to zero past it. Dealers who sell 0DTE options have to hedge their delta exposure mechanically, and because gamma is so concentrated, the hedging volume is too.
When 0DTE call buyers pile into an OTM strike, dealers selling those calls accumulate short gamma. As spot grinds toward the strike, the dealers' delta exposure changes faster and faster, forcing them to buy in size to stay neutral. That mechanical buying is what produces the famous "gamma squeeze" into call walls on green days. The same flow runs in reverse on red days at put walls.
What you see on the tape
- Pin-and-extend behavior. Spot drifts toward the nearest big-OI 0DTE strike, then either pins for the rest of the day or breaks decisively. The middle ground — slow drift past — almost never happens.
- IV crush on close. 0DTE IV is high pre-open and collapses by 16:00 as time-to-expiry dies. Short-premium structures that survive the open often pay full theta in the last 90 minutes.
- Range expansion after lunch. Once the 11:00 ET auction sets the day's range, 0DTE positioning typically pulls spot back toward the middle until 14:00, then expands again as gamma hedging unwinds.
The dealer's problem
Dealers don't want gamma risk. They want to be flat. So they hedge constantly — but each hedge moves spot, which moves their delta, which forces another hedge. In a high-0DTE regime, this loop is the dominant intraday flow. Studies from CBOE and academic groups put the dealer hedging share of SPX volume at 25–40% on a typical day. It's the elephant in the room.
What this means for non-0DTE traders
Even if you don't touch 0DTE, the gamma surface it creates determines whether your swing trade sees a smooth trend or a chop-chop sideways tape. A long-gamma SPX day (dealers net long gamma from outstanding 0DTE) looks like a 25-handle range. A short-gamma day looks like a 60-handle range. Same VIX number, different lived experience.
GEXRadar's 0DTE filter separates the same-day chain from longer-dated to show you the dealer position you'll actually trade against today. The longer-dated GEX matters for swing context; 0DTE matters for the next two hours.
Trading takeaways
- Mark the largest 0DTE call wall and put wall before the open. These are your intraday magnet levels.
- The gamma flip on the 0DTE chain is more actionable than the cross-expiry flip — it tells you the regime today.
- If the 0DTE put wall breaks, expect cascade. Dealer hedging amplifies the move because below the put wall there's no mechanical buyer.
- Don't fade a 0DTE breakout in the first hour. The hedging flow that drives the break is at its strongest from 9:30 to 10:30 ET.